/**
 * Copyright 2010-present Facebook.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.twodstar.selfie;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import android.os.AsyncTask;


public class SntpClient 
{

    private static final int ORIGINATE_TIME_OFFSET = 24;
    private static final int RECEIVE_TIME_OFFSET = 32;
    private static final int TRANSMIT_TIME_OFFSET = 40;
    private static final int NTP_PACKET_SIZE = 48;

    private static final int NTP_PORT = 123;
    private static final int NTP_MODE_CLIENT = 3;
    private static final int NTP_VERSION = 3;

    // Number of seconds between Jan 1, 1900 and Jan 1, 1970
    // 70 years plus 17 leap days
    private static final long OFFSET_1900_TO_1970 = ((365L * 70L) + 17L) * 24L * 60L * 60L;

    // system time computed from NTP server response
    private long mNtpTime;

    // value of SystemClock.elapsedRealtime() corresponding to mNtpTime
    private long mNtpTimeReference;

    // round trip time in milliseconds
    private long mRoundTripTime;
    
     
    private static boolean m_IsSuccessful = false; 
    private static long m_RecordedUTC_Time = 0;
    private static long m_RecordedSystemTime = 0;
    
    

    /*
     * exmaple usage
    SntpClient client = new SntpClient();
    if (client.requestTime("pool.ntp.org", 30000)) 
    {
        long now = client.getNtpTime() + System.nanoTime() / 1000
                - client.getNtpTimeReference();
        Date current = new Date(now);
        System.out.println(current.toString());
    }
    */

    /**
     * Sends an SNTP request to the given host and processes the response.
     *
     * @param host
     *            host name of the server.
     * @param timeout
     *            network timeout in milliseconds.
     * @return true if the transaction was successful.
     */
    
    private static SntpClient m_Client = null;
    
    
    public static long GetTimeUTC()
    {
    	long Ret = 0;
    	if(m_Client == null)
    	{
    		m_Client = new SntpClient();
    		m_IsSuccessful = false;
    		
    		m_Client.requestTime("pool.ntp.org", 30000);
    		
    		if(m_IsSuccessful)            
    		{
            	
    			Ret = m_RecordedUTC_Time;
            }
    		else
    		{
    			Ret = System.currentTimeMillis();
    		}
            
    	}
    	else if(m_IsSuccessful)
    	{
    		Ret = m_RecordedUTC_Time + (System.currentTimeMillis() - m_RecordedSystemTime);
    	}
    	else
    	{
    		m_Client.requestTime("pool.ntp.org", 30000);
    		if(m_IsSuccessful)
            {
            	m_IsSuccessful = true;
            	m_RecordedUTC_Time = m_Client.getNtpTime();
            	m_RecordedSystemTime = System.currentTimeMillis();   	               
                
            	Ret = m_RecordedUTC_Time;
            }
    		else
    		{
    			PBUtility.LOG("time goes back to phone settings");
    			Ret = System.currentTimeMillis();
    		}
    	}
    	return Ret;
        
        //return 0;
    }
    
    public void requestTime(final String host, final int timeout)
    {
    	AsyncTask<Void, Void, String > task = new AsyncTask<Void, Void, String>() 
        {
        	 @Override
        	 public void onPostExecute(String citations) 
        	 {
        		
        	 }
        	 

            @Override
            protected String doInBackground(Void... voids) 
            {
            	try 
            	{

            	DatagramSocket socket = new DatagramSocket();
            	socket.setSoTimeout(timeout);
            	InetAddress address = InetAddress.getByName(host);
            	byte[] buffer = new byte[NTP_PACKET_SIZE];
            	DatagramPacket request = new DatagramPacket(buffer, buffer.length,
            		address, NTP_PORT);

            	// set mode = 3 (client) and version = 3
            	// mode is in low 3 bits of first byte
            	// version is in bits 3-5 of first byte
            	buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);

            	// get current time and write it to the request packet
            	long requestTime = System.currentTimeMillis();
            	long requestTicks = System.nanoTime() / 1000;
            	writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime);

            	socket.send(request);

            	// read the response
            	DatagramPacket response = new DatagramPacket(buffer, buffer.length);
            	socket.receive(response);
            	long responseTicks = System.nanoTime() / 1000;
            	long responseTime = requestTime + (responseTicks - requestTicks);
            	socket.close();

            	// extract the results
            	long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);
            	long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
            	long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);
            	long roundTripTime = responseTicks - requestTicks
            		- (transmitTime - receiveTime);
            	// receiveTime = originateTime + transit + skew
            	// responseTime = transmitTime + transit - skew
            	// clockOffset = ((receiveTime - originateTime) + (transmitTime -
            	// responseTime))/2
            	// = ((originateTime + transit + skew - originateTime) +
            	// (transmitTime - (transmitTime + transit - skew)))/2
            	// = ((transit + skew) + (transmitTime - transmitTime - transit +
            	// skew))/2
            	// = (transit + skew - transit + skew)/2
            	// = (2 * skew)/2 = skew
            	long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime)) / 2;
            	// if (Config.LOGD) Log.d(TAG, "round trip: " + roundTripTime +
            	// " ms");
            	// if (Config.LOGD) Log.d(TAG, "clock offset: " + clockOffset +
            	// " ms");

            	// save our results - use the times on this side of the network
            	// latency
            	// (response rather than request time)
            	mNtpTime = responseTime + clockOffset;
            	mNtpTimeReference = responseTicks;
            	mRoundTripTime = roundTripTime;
            	
            	m_RecordedUTC_Time = m_Client.getNtpTime();
            	m_RecordedSystemTime = System.currentTimeMillis();
            	
            	PBUtility.LOG("network time: " + m_RecordedUTC_Time);
            	PBUtility.LOG("phone time: " + m_RecordedSystemTime);
            	
            	} 
            	catch (Exception e) 
            	{
            		if(e != null && e.getMessage() != null)
            			PBUtility.LOG(e.getMessage());
            		return "false";
            	}
            	
            	m_IsSuccessful = true;
				return "true";              
              
            }
            
        };

        task.execute();
		
    }

    /**
     * Returns the time computed from the NTP transaction.
     *
     * @return time value computed from NTP server response.
     */
    public long getNtpTime() {
        return mNtpTime;
    }

    /**
     * Returns the reference clock value (value of
     * SystemClock.elapsedRealtime()) corresponding to the NTP time.
     *
     * @return reference clock corresponding to the NTP time.
     */
    public long getNtpTimeReference() {
        return mNtpTimeReference;
    }

    /**
     * Returns the round trip time of the NTP transaction
     *
     * @return round trip time in milliseconds.
     */
    public long getRoundTripTime() {
        return mRoundTripTime;
    }

    /**
     * Reads an unsigned 32 bit big endian number from the given offset in the
     * buffer.
     */
    private long read32(byte[] buffer, int offset) {
        byte b0 = buffer[offset];
        byte b1 = buffer[offset + 1];
        byte b2 = buffer[offset + 2];
        byte b3 = buffer[offset + 3];

        // convert signed bytes to unsigned values
        int i0 = ((b0 & 0x80) == 0x80 ? (b0 & 0x7F) + 0x80 : b0);
        int i1 = ((b1 & 0x80) == 0x80 ? (b1 & 0x7F) + 0x80 : b1);
        int i2 = ((b2 & 0x80) == 0x80 ? (b2 & 0x7F) + 0x80 : b2);
        int i3 = ((b3 & 0x80) == 0x80 ? (b3 & 0x7F) + 0x80 : b3);

        return ((long) i0 << 24) + ((long) i1 << 16) + ((long) i2 << 8)
                + (long) i3;
    }

    /**
     * Reads the NTP time stamp at the given offset in the buffer and returns it
     * as a system time (milliseconds since January 1, 1970).
     */
    private long readTimeStamp(byte[] buffer, int offset) {
        long seconds = read32(buffer, offset);
        long fraction = read32(buffer, offset + 4);
        return ((seconds - OFFSET_1900_TO_1970) * 1000)
                + ((fraction * 1000L) / 0x100000000L);
    }

    /**
     * Writes system time (milliseconds since January 1, 1970) as an NTP time
     * stamp at the given offset in the buffer.
     */
    private void writeTimeStamp(byte[] buffer, int offset, long time) {
        long seconds = time / 1000L;
        long milliseconds = time - seconds * 1000L;
        seconds += OFFSET_1900_TO_1970;

        // write seconds in big endian format
        buffer[offset++] = (byte) (seconds >> 24);
        buffer[offset++] = (byte) (seconds >> 16);
        buffer[offset++] = (byte) (seconds >> 8);
        buffer[offset++] = (byte) (seconds >> 0);

        long fraction = milliseconds * 0x100000000L / 1000L;
        // write fraction in big endian format
        buffer[offset++] = (byte) (fraction >> 24);
        buffer[offset++] = (byte) (fraction >> 16);
        buffer[offset++] = (byte) (fraction >> 8);
        // low order bits should be random data
        buffer[offset++] = (byte) (Math.random() * 255.0);
    }
}


